3 Answers
3

This article has an interview with a scientist that works for the company that makes B-T-F Iodophor. He says that as long as the solution as the color, it should work. However he suggests making a new batch after 24 hours maximum.

Like you mentioned it seems rather impractical to reuse Iodophor beyond the 18 hour window that you normally get. Once it has been diluted to the recommended to 12 parts per million and you've used it. Theoretically you could store it in a plastic bucket with very little head space and reuse the santizer next time you need it.

But I still wouldn't trust it, Iodophor seems to leech in to the plastic over time. i.e., it turns the plastic brown. That said, I do keep a spray bottle at about 50 ppm around the house for when I need to spray down a carboy opening or some random equipment. (A practice I picked up from a local brewery)

My typical use for large batches of sanitizer is to just use it for the couple of hours I need it and then pitch it out.

I think it is reusable so long as you store it in an air tight container. This is because the active ingredient will evaporate. You can test this at home by making up as small amount of solution that is slightly brown in colour and leaving it for about a day in an open container. It will turn clear.